Corrosion control compositions and methods of mitigating corrosion

ABSTRACT

Corrosion inhibitor compositions are provided that can include a mixture of one or more transition metals, one or more organic phosphates, one or more inorganic phosphates, optionally a dispersant, and hydroxyphosphono acetic acid and/or salts thereof. Methods of mitigating or inhibiting corrosion of housing or conduits containing aqueous mediums are also disclosed. The methods can include the steps of pretreating the metal conduit with a mixture of one or more transition metals, one or more organic phosphates, one or more inorganic phosphates, and hydroxyphosphono acetic acid, introducing an aqueous medium into the metal conduit, and injecting a mixture of one or more transition metals, one or more organic phosphates, one or more inorganic phosphates, and hydroxyphosphono acetic acid and/or salts thereof into the aqueous medium.

CROSS-REFERENCE TO RELATED APPLICATIONS

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FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

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THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

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REFERENCE TO A SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTINGCOMPACT DISC APPENDIX

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BACKGROUND OF THE INVENTION

1. Field of the Invention

The disclosure pertains to compositions and methods useful forcontrolling corrosion. In particular, the disclosure pertains tocorrosion control compositions and methods of mitigating corrosion ofmetals in corrosive aqueous systems.

2. Description of the Related Art

Corrosion of metal surfaces in aqueous media has long been a problem forindustries such as the oil and gas industry, food/beverage industry, andwash/sanitizing industry. For example, it is well known that during theproduction of oil and gas several other corrosive components are presentsuch as brines, organic acids, carbon dioxide, hydrogen sulfide, andmicroorganisms. These aggressive constituents can cause severe corrosionas evidenced by surface pitting, embrittlement, and general loss ofmetal. The metallic surfaces can be composed of high alloy steelsincluding chrome steels, ferritic alloy steels, austenitic stainlesssteels, precipitation-hardened stainless steels, and high nickel contentsteels, but most often the less expensive carbon steels are utilized incombination with corrosion inhibitors or coatings. This problem is evenmore troublesome in deep-sea operations where replacement of corrodedequipment is difficult and costly.

Sea water is a highly corrosive media. When sea water is brought intocontact with various metals, such as during transportation of the seawater in metal pipelines, corrosion of the metal can occur. The use ofoxygen scavengers has been suggested as a way to successfully preventcorrosion in pipelines exposed to sea water. Despite the relativeeffectiveness, this solution has two main drawbacks. First, it demandsthe construction of a degasification unity at each pumping station,which will represent a high initial investment. Second, the solutionrequires large amounts of chemicals since it is necessary to completelyneutralize the entire amount of oxygen dissolved in the water each timeit passes through a pumping station considering that these operationsare carried out at open air. Although attempts have been made to reduceor prohibit corrosion in metals exposed to sea water, it remainsextremely challenging to control the corrosion of metal surfacescontacting such highly corrosive media.

In the food/beverage and wash/sanitizing industry, solutions such assodium hypochlorite solutions are commonly used and are highly effectiveas bleaches and sanitizers for cleaning a variety of surfaces. However,sodium hypochlorite solutions are corrosive to many treated surfaces, inparticular, metal surfaces become highly corroded.

There are several mechanisms responsible for corrosion of metals. Incorrosive water systems, the overall corrosion rate is controlled by thereduction of oxygen inhibiting the cathodic reaction. However, the mostrobust and cost effective water treatment programs include both anodicand cathodic inhibitors to block reactions at both the anode and thecathode.

Anodic inhibitors suppress the rate of metal ions being transferred intothe aqueous environment while cathodic inhibitors act through thedevelopment of a barrier film that reduces the ability of oxygen todiffuse to the metal surface.

Despite the availability of a variety of corrosion inhibitors, therestill exists a need for improved compounds and methods for providingcorrosion inhibition, in addition to a need to develop less expensive,high performance corrosion inhibitors, including chemistries thatprovide environmental benefits, health benefits (e.g., handling andmanufacturing), manufacturing energy reduction, and reduction in wastegeneration.

BRIEF SUMMARY OF THE INVENTION

Corrosion inhibitor compositions are provided that can comprise amixture of one or more transition metals, one or more organicphosphates, one or more inorganic phosphates, and hydroxyphosphonoacetic acid and/or salts thereof.

Methods of mitigating corrosion of housings or conduits containing anaqueous medium are also disclosed. The methods can include the steps ofproviding a metal conduit for the aqueous medium, introducing an aqueousmedium into the metal conduit, injecting a mixture of an effectiveamount of one or more transition metals, one or more organic phosphates,and one or more inorganic phosphates into the aqueous medium, andinjecting an effective amount of hydroxyphosphono acetic acid and/orsalts thereof into the aqueous medium.

In certain aspects, the methods can further include treating the metalconduit with an effective amount of a mixture of one or more transitionmetals, one or more organic phosphates, and one or more inorganicphosphates before the aqueous medium is introduced into the metalconduit and treating the metal conduit with an effective amount ofhydroxyphosphono acetic acid and/or salts thereof before the aqueousmedium is introduced into the metal conduit.

The foregoing has outlined rather broadly the features and technicaladvantages of the present disclosure in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the disclosure will be describedhereinafter that form the subject of the claims. It should beappreciated by those skilled in the art that the conception and thespecific embodiments disclosed may be readily utilized as a basis formodifying or designing other embodiments for carrying out the samepurposes of the present disclosure. It should also be realized by thoseskilled in the art that such equivalent embodiments do not depart fromthe spirit and scope of the disclosure as set forth in the appendedclaims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

A detailed description of the invention is hereafter described withspecific reference being made to the drawings in which:

FIG. 1 shows a chart depicting the LPR results of an experiment run inthe presence or absence of Corrosion Inhibitor 1 as a corrosion in seawater and the pH effect;

FIG. 2 shows a chart depicting the LPR results of an experiment runusing Corrosion Inhibitor 1 in the presence or absence of CorrosionInhibitor 2 under adjusted pH and the test coupons were precoated usingCorrosion Inhibitor 1 without pH adjustment;

FIG. 3 shows a chart depicting the LPR results of an experiment usingCorrosion Inhibitor 1 in the presence or absence of Corrosion Inhibitor2 and/or Corrosion Inhibitor 3 under adjusted pH where the test couponswere precoated using Corrosion Inhibitor 1 without pH adjustment;

FIG. 4 shows a chart depicting the LPR results of an experiment usingCorrosion Inhibitor 1 in the presence of Corrosion Inhibitor 3 underadjusted pH of 8.5 where the test coupons were precoated using CorrosionInhibitor 1 and optionally Corrosion Inhibitor 3 with a pH adjustment to8.5;

FIG. 5 shows a chart depicting the LPR results of an experiment run in asea water environment under adjusted pH where the test coupons wereprecoated using Corrosion Inhibitor 1 and optionally Corrosion Inhibitor3 with a pH adjustment to 8.5;

FIG. 6 shows a chart depicting the LPR results of an experiment run in asea water environment under adjusted pH where the test coupons wereprecoated using Corrosion Inhibitor 1 and Corrosion Inhibitor 3 with apH adjustment to 8.5;

FIG. 7 shows a chart depicting the LPR results of an experiment run withsea water from the Pacific Ocean under adjusted pH where the testcoupons were precoated using Corrosion Inhibitor 1 and CorrosionInhibitor 3 with a pH to 8.5; and

FIG. 8 shows a chart depicting the LPR results of an experiment run withsea water from the Atlantic Ocean under adjusted pH where the testcoupons were precoated using Corrosion Inhibitor 1 and CorrosionInhibitor 3 with a pH adjustment to 8.5.

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure provides a treatment including compositions andmethods useful for inhibiting corrosion of metal surfaces in contactwith aqueous media. This treatment eliminates the use of an oxygenscavenger and it also eliminates the need to construct degasificationfacilities.

As used herein, “corrosion inhibitor” is intended to refer to at leastone of, or any combination of, the disclosed corrosion inhibitors,corrosion inhibitor intermediates, and corrosion inhibitor productformulations.

In an aspect, a corrosion inhibitor of the present disclosure caninclude multiple components. For example, the corrosion inhibitor caninclude a mixture of any transition metal, an organic phosphate, and aninorganic phosphate. This mixture can be present in the corrosioninhibitor in amounts ranging from about 2 ppm to about 500 ppm. Forexample, the mixture can be present in amounts ranging from about2-about 5 ppm, or about 5-about 20 ppm, or about 30-about 50 ppm, orabout 70-about 100 ppm, or about 200-about 500 ppm, or any range orsub-range thereof. In one embodiment, the mixture includes zinc, o-PO₄,and PSO. This mixture is referred to herein as “Corrosion Inhibitor 1”While a corrosion inhibitor comprising a mixture of any transitionmetal, an organic phosphate, and an inorganic phosphate can includethese three components in any ratio, 50 ppm of Corrosion Inhibitor 1would include 3 ppm of active zinc, 12 ppm of active o-PO₄, and 4.7 ppmof active PSO.

Transition metals are commonly known in the art. An example of atransition metal is zinc. Organic phosphates are also commonly known inthe art and examples of such are phospheno, phosphono, and phosphonatecontaining compounds. Similarly, inorganic phosphates are commonly knownin the art and an example of such is orthophosphate or PO₄.

The presently disclosed corrosion inhibitor can further comprise adispersant. The dispersant can be, for example, any polymer, copolymer,terpolymer, etc., comprising acrylic acid or acrylamide with sulfonatedmonomers. An example of such a dispersant is a copolymer of acrylicacid/2-acrylamido-2-methylpropane sulfonic acid (AMPS). Another exampleof such a dispersant is a copolymer of acrylic acid/acrylamide. Anadditional example of such a dispersant is a terpolymer of acrylicacid/acrylamide/sulfonated acrylamide. All monomer ratios in each of thepresently disclosed copolymers or terpolymers are intended to be coveredby the present disclosure. In one aspect, the dispersant is a terpolymercomprising acrylic acid/acrylamide/sulfonated acrylamide in a monomerratio of about 40/about 20/about 40. This specific embodiment isreferred to herein as “Corrosion Inhibitor 2.” 50 ppm of CorrosionInhibitor 2 would comprise 14.5 ppm of active terpolymer.

The dispersant can be present in the corrosion inhibitor in amountsranging from about 1 to about 50 ppm. For example, the dispersant can bepresent in amounts ranging from about 1-about 10 ppm, or about 5-about20 ppm, or about 30-about 50 ppm, or any range or sub-range thereof. Inone embodiment, the dispersant is Corrosion Inhibitor 2 and is presentin the corrosion inhibitor composition in an amount of about 5 ppm.

Additionally, the corrosion inhibitor of the present disclosure cancomprise hydroxyphosphono acetic acid and/or salts thereof. Thehydroxyphosphono acetic acid and/or salts thereof can be present in thecorrosion inhibitor in amounts ranging from about 1 to about 50 ppm. Forexample, the hydroxyphosphono acetic acid and/or salts thereof can bepresent in amounts ranging from about 1-about 5 ppm, about 5-about 10ppm, about 10-about 25 ppm, or about 25-about 50 ppm, or any range orsub-range thereof. As referred to herein the present application,“Corrosion Inhibitor 3” is hydroxyphosphono acetic acid. 50 ppm ofCorrosion Inhibitor 3 would include 25 ppm of active hydroxyphosphonoacetic acid. In an aspect, Corrosion Inhibitor 3 can be present in thecorrosion inhibitor composition in an amount of about 2.5 ppm.

Thus, in one aspect, the presently disclosed corrosion inhibitor cancomprise a mixture of any transition metal, an organic phosphate, aninorganic phosphate, a dispersant, and hydroxyphosphono acetic acidand/or salts thereof. It thus follows that in one aspect, the corrosioninhibitor composition can comprise Corrosion Inhibitor 1, CorrosionInhibitor 2, and Corrosion Inhibitor 3.

In another aspect, the presently disclosed corrosion inhibitor cancomprise a mixture of any transition metal, an organic phosphate, aninorganic phosphate, and hydroxyphosphono acetic acid and/or saltsthereof. It thus follows that in one aspect, the corrosion inhibitorcomposition can comprise Corrosion Inhibitor 1 and Corrosion Inhibitor3.

In yet a further aspect, the presently disclosed corrosion inhibitor cancomprise a mixture of any transition metal, an organic phosphate, and aninorganic phosphate. It thus follows that in one aspect, the corrosioninhibitor composition comprises only Corrosion Inhibitor 1.

In certain aspects of the present disclosure, the treatment contemplatedby the present disclosure can include an initial pretreatment of themetal surface of the system incorporating a pre-passivation step usingabout 100 ppm of a mixture of zinc, an organic phosphate, and aninorganic phosphate plus about 50 ppm of hydroxyphosphono acetic acid.Sea water can be introduced into the metal system and the pH of the seawater can optionally be adjusted to about 8.5 using lime, followed by awater treatment step using about 5 ppm of a mixture of zinc, an organicphosphate, and an inorganic phosphate, plus about 2.5 ppmhydroxyphosphono acetic acid.

For example, a method of mitigating corrosion according to the presentdisclosure can include providing a metallic housing or conduit that willcontain an aqueous medium. The metal conduit can be pretreated with aneffective amount of a mixture of one or more transition metals, one ormore organic phosphates, and one or more inorganic phosphates. The metalconduit can also be pretreated with an effective amount ofhydroxyphosphono acetic acid and/or salts thereof. After thesepretreatment steps, an aqueous medium can be introduced into the metalor housing. After introduction of the aqueous medium, a mixture of aneffective amount of one or more transition metals, one or more organicphosphates, and one or more inorganic phosphates can be injected intothe aqueous medium. Finally, an effective amount of hydroxyphosphonoacetic acid and/or salts thereof can be injected into the aqueousmedium. Thereby, corrosion of the metal conduit or housing will bemitigated or prevented.

In certain aspects of this method, the pH of the aqueous medium can beadjusted to about 8.5 by adding lime or soda ash thereto.

In certain aspects, the effective amount of the mixture of one or moretransition metals, one or more organic phosphates, and one or moreinorganic phosphates in the initial pretreating step is about 100 ppmand the effective amount of hydroxyphosphono acetic acid and/or saltsthereof in the initial pretreating step is about 50 ppm.

Moreover, in certain aspects, the effective amount of the mixture of oneor more transition metals, one or more organic phosphates, and one ormore inorganic phosphates in the injecting step is from about 5 ppm toabout 20 ppm and the effective amount of hydroxyphosphono acetic acidand/or salts thereof in the injecting step is from about 2.5 ppm toabout 10 ppm.

In certain aspects, the aqueous medium is sea water. Also, in certainaspects, the one or more transition metals comprises zinc.

According to the present disclosure, the selection of the appropriatecombination of components, and amounts of components, can be based upon,for example, the type of aqueous media causing the corrosion and/or thetype of corrosion. In this regard, if the aqueous media is alkaline orhas a basic pH, one may select a corrosion inhibitor comprising amixture of any transition metal, an organic phosphate, an inorganicphosphate, a dispersant, and hydroxyphosphono acetic acid and/or saltsthereof.

Dissolved phosphates of the present corrosion inhibitor assist in thecorrosion inhibition process. However, in an alkaline media, thephosphates can precipitate from the solution and are thus rendereduseless for their desired corrosion inhibition purposes. For example, inan alkaline media, if the corrosion inhibitor comprises a mixture of atransition metal such as zinc, an organic phosphate, an inorganicphosphate, and hydroxyphosphono acetic acid and/or salts thereof, zincphosphate can form and/or calcium phosphate can form. The zincphosphates and calcium phosphates will precipitate and thus, thesephosphates will lose their corrosion inhibition properties. Thus, in analkaline media, one can include a dispersant in the corrosion inhibitor.That is, the corrosion inhibitor can comprise any transition metal, anorganic phosphate, an inorganic phosphate, a dispersant, and optionallyhydroxyphosphono acetic acid and/or salts thereof. The dispersantcomponent will assist in blocking the formation of the undesiredphosphate precipitates and will thus allow the phosphates to remaindissolved and perform their function as corrosion inhibitors.

It follows then, in an acidic media, there may be no need to include adispersant component in the corrosion inhibitor, such as CorrosionInhibitor 2. In general, the lower the pH of the aqueous media, the lesscorrosive the media becomes.

Thus, the present inventors have discovered a synergistic combination ofa mixture of any transition metal, an organic phosphate, an inorganicphosphate, optionally a dispersant, and hydroxyphosphono acetic acidand/or salts thereof. Lime or soda ash is useful for lowering the pH ofthe aqueous media. In turn, this will lower the effective amount of themixture of the transition metal, the organic phosphate, and theinorganic phosphate necessary to effectively inhibit or preventcorrosion. Thereby, the overall cost of the treatment will bedramatically reduced as soda ash or lime is significantly less expensivethan the mixture of transition metal, organic phosphate, and inorganicphosphate.

One type of unique aqueous media is sea water. This media isdramatically different than other aqueous media, such as municipalwater, because it has a large amount of total dissolved solids (TDS),for example. In activities such as mining, one difficulty that can beencountered is a shortage of water supply. In Chile, in order toovercome this difficulty, some mining companies have proposed totransport water from Pacific Ocean up to the mountains using mild steelpipelines. In such a situation, studies need to be carried out toidentify a proper corrosion inhibitor for the sea water media and due tothe complexity and uniqueness of sea water, this is an intensive task.As can be seen from the examples in the present specification, allaspects of the presently claimed corrosion inhibitor were successful inmitigating, inhibiting and/or preventing corrosion of metals exposed tosea water.

Furthermore, different types of corrosion can occur and this can alsohelp determine which components should be included in the corrosioninhibitor. For example, “pitting corrosion,” or “pitting,” is alocalized form of corrosion that causes or develops craters orpotentially small holes in the metal. Essentially, the corrosionpenetrates deeper and deeper into the metal in a small, localized area,causing loss of metal. The inner surface, or portion of the surfacecontacting the corrosive media that comprises the pitting, usuallybecomes anodic, while a potentially large area of the remainder of theinner metal surface becomes cathodic. Where the surface to be treatedincludes pitting, one may choose to include hydroxyphosphono acetic acidand/or salts thereof, in the corrosion inhibitor composition. Thehydroxyphosphono acetic acid and/or salts thereof can deposit over, orcover, salts formed in the crater or pit and block further pitting.

As can be seen in the examples disclosed herein, the present inventorshave discovered a synergistic combination of ingredients that inhibit orprevent pitting, as well as other types of corrosion. In certainaspects, the synergy is between a mixture of a transition metal such aszinc, an organic phosphate, an inorganic phosphate, and hydroxyphosphonoacetic acid and/or salts thereof.

Thus, in one aspect, where pitting corrosion is involved, a corrosioninhibitor according to the present disclosure can comprise a mixture ofa transition metal, an organic phosphate, an inorganic phosphate, andhydroxyphosphono acetic acid and/or salts thereof. In another aspect,the corrosion inhibitor can comprise a mixture of a transition metal, anorganic phosphate, an inorganic phosphate, a dispersant, andhydroxyphosphono acetic acid and/or salts thereof.

The presently disclosed corrosion inhibitor can be injected into theaqueous system by any means known in the art. For example, the inhibitorcan be injected via a chemical metering pump into aqueous system. Otheracceptable methods of injection include pretreating/precoating the metalsurfaces before exposure to the corrosive aqueous media, continuousinjection, or batch treating. Continuous injection may be performedwhere appropriate chemical injection equipment is available in the fieldalong with chemical storage tanks. Otherwise, the chemical may betreated using a specialized treatment vehicle which applies a largechemical dosage at long time intervals, usually every one to two weeks,and in certain cases, monthly. Batch application may be performedthrough the use of a treating truck comprising a storage tank containingthe corrosion inhibitor(s) (and optionally other chemicals) and a largewater tank. The treating truck travels to field locations and treatsindividual sites.

EXAMPLES

Procedures were set up to test the effectiveness of the presentlydisclosed corrosion inhibitors in mitigating corrosion in steel underaerated sea water environments. Precoating/pretreating of the metalsurface using 100 ppm of a mixture of Corrosion Inhibitor 1 (whichincludes 6 ppm active zinc, 24 ppm active o-PO₄, and 9.4 ppm activePSO), and 50 ppm of Corrosion Inhibitor 3 (which includes 25 ppm ofactive terpolymer) was tested in connection with sea water having a pHof 8.5. Once the metal surface was passivated, protection againstcorrosion was supplied by treating aerated sea water using CorrosionInhibitor 1 and Corrosion Inhibitor 3. The dosage of corrosioninhibitors varied according to water composition and the specificcharacteristics of each system.

As can be seen below and in the drawing figures, successful results wereachieved in synthetic sea water with a pH of 8.5 at room temperatureusing 5 ppm of Corrosion Inhibitor 1 and 2.5 ppm of Corrosion Inhibitor3. The use of sea water samples from the Atlantic Ocean (Rio de Janeiro)required higher dosages, e.g. Corrosion Inhibitor 1 was dosed between10-20 ppm and the Corrosion Inhibitor 3 was dosed between 5-10 ppm at an8.5 pH.

Tests were also carried out using synthetic sea water, which wasproduced by adding ions in demineralized water to reach the compositionfound in an analysis of a sample taken from a collecting point of thePacific Ocean off of Chile. Validation trials were performed using realsamples of sea water from the Pacific Ocean collected at this collectingpoint off of Chile or samples of sea water collected from the AtlanticOcean off of Rio de Janeiro at Barra da Tijuca beach.

Tubular-shaped test coupons made of C1018 mild carbon steel were usedfor the electrochemical and weight loss measurements. Test coupondimensions were:

outside diameter: 12.0 mm;

inside diameter: 6.0 mm;

length: 8.0 mm.

In certain aspects, the test coupons received a surface pretreatmentbefore use. Where the test coupons were pretreated, the test couponswere dipped for two minutes in acetone, two minutes in xylene, and thenan additional two minutes in acetone in order to remove any residual,oily substances. The test coupons were then immersed into concentratedhydrochloric acid (36%) for five minutes. Lastly, the test coupons werecopiously rinsed with distilled water and inserted into the rotatingcylinder electrode support.

The corrosion inhibitors and auxiliaries selected for this study were:

-   -   A. A mixture of zinc, an organic phosphate (PSO), and an        inorganic phosphate (o-PO₄) (“Corrosion Inhibitor 1”)    -   B. Hydroxyphosphono acetic acid (“Corrosion Inhibitor 3”)    -   C. Dispersant comprising a terpolymer of acrylic        acid/acrylamide/sulfonated acrylamide (“Corrosion Inhibitor 2”)

In Drawing FIGS. 1-8, “Corrosion 1=Corrosion Inhibitor 1,” “Corrosion2=Corrosion Inhibitor 2,” and “Corrosion 3=Corrosion Inhibitor 3.”

In certain experiments, the pH of the sea water was adjusted using lime(Ca(OH)₂). Electrochemical polarization measurements were performedusing an Autolab PGSTAT 302N driven by NOVA 1.8 Software. All trialswere carried out at room temperature.

For corrosion inhibition trials, four conventional glass cells (1000 cm³in volume, assembled in parallel) were used for the polarizationstudies. All potential measurements were performed with sea water; ametallic stainless steel object was used as a pseudo-reference electrodeand a stainless steel rod was used as a counter electrode.

All experiments for corrosion rate measurement, as well as for corrosioninhibitor selection, were carried out using linear polarizationresistance technique (LPR). LPR is one of the most commonly used methodsto measure corrosion rate. It is a DC electrochemical technique and istypically based on the imposition of a small voltage to the electrodes,(−10 mV to +10 mV) around the Open Circuit Potential (OCP). If thepotential is raised above the free corrosion potential (Ecorr), themetal dissolution rate will increase. Conversely, if the potential islowered, the rate will decrease. The LPR technique assumes that theexponential anodic (i.e. potential above Ecorr), and the cathodic (i.e.potential below Ecorr) polarization curves approximate to a straightline close to the free corrosion potential (OCP).

The corrosion rate can then be derived from the theoretical Stern andGeary² analysis of polarization curves and Faraday's Law.

Another way to follow corrosion rate is through mass loss balance. Thistechnique is suitable for both generalized and localized corrosion andcan be described as follows. The tubular test coupons received a surfacetreatment after each electrochemical experiment in order to remove anycorrosion product eventually deposited on the surface before beingweighed. The test coupons were copiously rinsed with water, smoothlybrushed, and then immersed into concentrated hydrochloric acid for 5seconds. Finally, the test coupons were copiously rinsed with distilledwater, dried, and weighed.

Once the corrosion rate (CR) is known for a specific sample of water,corrosion inhibitor performance can be evaluated. Measurement of weightloss along with instantaneous electrochemical corrosion using LPR wascarried out keeping the rotating electrode at 2000 rpm. The assays werecarried in the presence or absence of a corrosion inhibitor. The percentprotection relative to blank samples can be determined for each chemicalaccording to the following equation:

Efficiency of inhibition (%)=((CR−CR_(CI))×100)/CR, wherein CR is thecorrosion rate without any treatment and CR_(CI) is the corrosion ratedetermined in the presence of a corrosion inhibitor.

Coating is a known mechanism of protection by which some anticorrosiveadditives work. This technique was tested in order to verify if improvedperformance of the presently disclosed corrosion inhibitors could beachieved. In these experiments, an RCE electrode was submerged into abath of sea water at room temperature containing particular embodimentsof the presently disclosed corrosion inhibitors. The electrode remainedin this condition under 2000 rpm stirring for 24 hours. During thistime, corrosion rate was not monitored and after the coating period, theelectrode was immediately submerged into the sea water medium with aspecified amount of a corrosion inhibitor and submitted to furtherelectrochemical and mass loss balance trials.

Diagnosis between localized (pitting) and general corrosion can beaccomplished through surface examination before and after each trial.This exam was recorded using a digital camera and microscopy with 40× or100× magnification lens. This qualitative method is extremely useful toevaluate the performance of corrosion inhibitors, especially whenlocalized corrosion or pitting is taking place.

Corrosion rate of mild steel submerged in untreated sea water wascompared with values obtained using different dosages of certainpresently disclosed corrosion inhibitors under different conditions,such as after prepassivation of the metal surface using the samecorrosion inhibitor. Corrosion rates were continuously measured usingthe LPR electrochemical technique until variation of the values was nolonger detected for a sufficient period of time, i.e. untilstabilization of corrosion the rate. Weight loss balance data were alsoused to confirm the LPR results.

Trials were carried out in order to evaluate if a localized corrosionprocess was due to the nature of water chemistry, and if it could beavoided during a precoating/pretreating step. Four trials were setup inparallel using sea water under different conditions as follows. Thefirst using 100 ppm of Corrosion Inhibitor 1, the second using 500 ppmof Corrosion Inhibitor 1, the third in absence of a corrosion inhibitorbut with pH adjusted to 8.45, and the fourth in the absence of corrosioninhibitor with pH adjusted to 9.03. All trials were monitored using LPRfor 66 hours. Coupons were weighed at the beginning and at the end ofthe trial after cleaning. Results are shown in Table 1 and FIG. 1.Visual analysis of the surface also helped to diagnose between localizedand generalized corrosion phenomena.

TABLE 1 Trial conditions and weight loss balance results in the presenceor absence of Corrosion Inhibitor 1 as corrosion inhibitor in sea waterand pH effect. Trial time 66 hours. Corrosion Inhibitor 1 Corrosion rateTrial (ppm) Initial pH Final pH (mpy)* 1 — 7.90 8.19 83.4 2 100 6.607.91 2.4 3 500 6.00** 7.55 2.7 4 — 8.45** 8.35 42.7 5 — 9.03** 8.84 15.5*Calculated based on mass loss balance **pH adjusted with Ca(OH)₂.

Visual examination of the surfaces of the electrode can indicate thepresence of localized or pitting corrosion that otherwise would not bedetected by LPR or mass loss balance techniques. The electrode surface,which was submerged into untreated sea water, presented clear signals oflocalized corrosion. This means that besides being very corrosive, thismedium can also rapidly damage the equipment. As can be noted from thedata, simply adjusting the pH is not enough to avoid localizedcorrosion. This treatment can only moderately reduce the generalizedcorrosion rate as observed by LPR measurement but the presence oflocalized corrosion certainly would compromise the lifetime of theequipment. The use of Corrosion Inhibitor 1 was very effective toprevent generalized corrosion. The corrosion rate measured by LPR can belower than 2 mpy using 100 ppm dosage and lower than 0.1 mpy using 500ppm dosage. This corrosion inhibitor also presented some efficiencyagainst localized corrosion, which is more clearly observed at 500 ppmdosage. In spite of this, such a high dosage could be impractical inthis system due to the high consumption that it would represent (around40,000 ton/year).

Since Corrosion Inhibitor 1 had the best performance against generalizedcorrosion but did not present completely satisfactory results againstlocalized corrosion, the treatment was modified in order to assure fullprotection to steel surfaces in a sea water environment. In order toaccomplish that objective, some trials using Corrosion Inhibitor 1 werecarried out under controlled pH conditions. Supplementary corrosioninhibitor components (Corrosion Inhibitor 2 and Corrosion Inhibitor 3)were also incorporated into the Corrosion Inhibitor 1 corrosioninhibitor treatment with the specific purpose of mitigating localizedcorrosion. These experiments are described in the following trials.

In the first of these modified trials, coupons were precoated using 100ppm of Corrosion Inhibitor 1 without pH adjustment for 24 h. Thissequence of tests was carried out using Corrosion Inhibitor 1 (20 ppm)in the presence or absence of Corrosion Inhibitor 2 (5 ppm) underadjusted pH of 8.5 or 9.0 using Ca(OH)₂. Coupons were weighed at thebeginning and at the end of the trial after cleaning. Results are shownin Table 2 and FIG. 2.

TABLE 2 Trial conditions and weight loss balance results using CorrosionInhibitor 1 (20 ppm) in the presence or absence of Corrosion Inhibitor 2(5 ppm) under adjusted pH. Coupons were precoated using CorrosionInhibitor 1 (100 ppm) without pH adjustment. Corrosion CorrosionInhibitor 1 Inhibitor 2 Adjusted Final Corrosion Trial (ppm) (ppm) pHpH* rate (mpy) 6 20 0 8.52 8.29 7.1 7 20 5 8.52 8.25 9.0 8 20 0 9.078.78 7.8 9 20 5 9.00 8.59 9.1 *After 64 hours trial.

All results were obtained using either the LPR technique or weight lossbalance indicated a good corrosion inhibition efficiency of CorrosionInhibitor 1 at 20 ppm. Results obtained at pH 8.5 and 9.0 in thepresence of Corrosion Inhibitor 1 (Trials 6 to 9) are significantlyimproved when they are compared to results obtained in absence ofCorrosion Inhibitor 1 even at controlled pH (Trials 4 and 5).

The Corrosion Inhibitor 2 showed an inhibition effect over localizedcorrosion. Images obtained either at pH 8.5 and 9.0 revealed a lowernumber of points of attack when this additive is used (Trials 7 and 9).The increased rate of corrosion observed in FIG. 2 for numbers 3 and 4are due to scaling that occurred at the higher pH of 9.

Corrosion Inhibitor 3 was also tested as a corrosion inhibitor auxiliaryspecifically applied to reduce localized corrosion. In these trials,coupons were precoated using 100 ppm of Corrosion Inhibitor 1 without pHadjustment for 24 h. Inhibitor dosages and experimental conditions aswell weight loss balance results are shown in Table 3. Results of LPRelectrochemical measurements are shown in FIG. 3.

TABLE 3 Experimental conditions and weight loss balance results usingCorrosion Inhibitor 1 (20 ppm) in the presence or absence of CorrosionInhibitor 2 and/or Corrosion Inhibitor 3 under adjusted pH. Couponsprecoated using Corrosion Inhibitor 1 (100 ppm) without pH adjustment.Corrosion Corrosion Corrosion Ad- Corrosion Inhibitor 1 Inhibitor 3Inhibitor 2 justed Final rate Trial (ppm) (ppm) (ppm) pH pH* (mpy) 10 2010 5 8.91 8.65 5.5 11 20 5 15 8.89 8.56 4.9 12 20 10 — 8.25 8.03 4.2*After 60 hours trial.

FIG. 3 shows LPR results using Corrosion Inhibitor 1 (20 ppm) in thepresence or absence of Corrosion Inhibitor 2 and/or Corrosion Inhibitor3 under adjusted pH. Coupons were precoated using Corrosion Inhibitor 1(100 ppm) without pH adjustment. An electrical contact problem occurredin the middle of the trial using Corrosion Inhibitor 1 (20ppm)+Corrosion Inhibitor 2 (15 ppm)+Corrosion Inhibitor 3 (10 ppm) andtherefore these LPR data are valid just up to 29 hours. The use ofCorrosion Inhibitor 3 promoted a clear improvement in global corrosioninhibition. Both LPR and weight loss balance results confirm thisobservation. Comparable tests are 9 with 10, and 7 with 12, whichrespectively were carried out under the same experimental conditions,but with the presence or absence of Corrosion Inhibitor 3. Corrosionrates measured by weight loss balance are significantly lower usingCorrosion Inhibitor 3.

The use of Corrosion Inhibitor 3 clearly reduced localized corrosion inmild steel under sea water environment upon visual inspection of thetest coupons as well. The surface of the coupon after chemical cleaningdid not present any clear signs of pitting. There were only slightchanges on the coupon surface observed after mechanical cleaning.

In order to confirm the efficiency of Corrosion Inhibitor 3, a set oflong term experiments was carried out. Four coupons were precoated usingCorrosion Inhibitor 1 (100 ppm) at controlled pH and optionallyCorrosion Inhibitor 3 was added at the beginning of the precoating step.Considering the result obtained in Trial 2, the pH was adjusted duringprepassivation in order to minimize any corrosion process that couldtake place during this step. After the prepassivation, coupons weresubmerged into pretreated sea water according to the conditions shown inTable 4. LPR data is shown in FIG. 4 and weight loss balance results areshown in Table 4.

TABLE 4 Experimental conditions and weight loss balance results usingCorrosion Inhibitor 1 in the presence of Corrosion Inhibitor 3 underadjusted pH. Coupons were precoated using Corrosion Inhibitor 1 (100ppm) and optionally Corrosion Inhibitor 3 (50 ppm) with pH adjustment to8.5. Corrosion Corrosion Ad- Corrosion Inhibitor Inhibitor justed Finalrate Trial Precoating 1 (ppm) 3 (ppm) pH pH* (mpy) 13 CR 1 at 100 ppm 2010 8.53 8.12 6.3 14 CR 1 at 100 ppm 5 2.5 8.49 8.07 3.8 15 CR 1 at 100ppm + 20 10 8.49 8.08 4.3 CR 3 at 50 ppm 16 CR 1 at 100 ppm + 5 2.5 8.508.09 5.3 CR 3 at 50 ppm *After 114 hours trial.

In the foregoing Table, CR 1=Corrosion Inhibitor 1 and CR 3=CorrosionInhibitor 3. Trials 13 to 16 reveal that the use of Corrosion Inhibitor1 along with Corrosion Inhibitor 3 is an efficient treatment to preventgeneralized corrosion in mild steel under sea water environment. Thistreatment does not require oxygen removal and therefore its applicationis simpler than deaeration followed by oxygen scavenger addition. LPRmeasurement showed that the protecting film was stable during the wholetrial period. In fact, a slight decrease in corrosion rate was observed,which reinforces this observation. Corrosion rate at the end of thetrial was lower than 5 mpy for all experiments including under reducedcorrosion inhibitor dosage (Trials 14 and 16). Small fluctuations incorrosion rate are in perfect agreement with temperature oscillationsdue to day/night cycle. Weight loss balance measurement also agreed withLPR data. Surface analysis of the coupons was carried out in order toverify the efficiency of this corrosion inhibitor combination againstlocalized corrosion. It was visually observed that there was no sign oflocalized corrosion in either of the test coupons including in thetrials using lower dosage (Trials 14 and 16).

Once a suitable treatment to prevent corrosion in a sea waterenvironment under air was developed to protect mild steel, it waspossible to consider the initial optimization of the system. Theprecoating film resistance against untreated sea water was studied aswell as the effect of Corrosion Inhibitor 3 during the precoating step.Results and experimental conditions are shown in Table 5 and FIG. 5.

TABLE 5 Experimental conditions and weight loss balance results in seawater environment under adjusted pH. Coupons were precoated usingCorrosion Inhibitor 1 (100 ppm) and optionally Corrosion Inhibitor 3 (50ppm) with pH adjustment to 8.5. Corrosion Corrosion Ad- CorrosionInhibitor Inhibitor justed Final rate Trial Precoating 1 (ppm) 3 (ppm)pH pH* (mpy) 17 CR 1 at 100 ppm + 2.5 1.25 8.50 8.14 8.4 CR 3 at 50 ppm18 CR 1 at 100 ppm + — — 8.50 8.10 17.1 CR 3 at 50 ppm 19 CR 1 at 100ppm 2.5 1.25 8.50 8.12 13.5 *After 63 hours trial.

In the foregoing Table, CR 1=Corrosion Inhibitor 1 and CR 3=CorrosionInhibitor 3. Trial 18 was carried out using untreated sea water underair atmosphere and it showed that the corrosion rate sharply increasesat the beginning of the trial and keeps at 12 mpy. This is an indicationthat the precoated film is not resistant enough to stay intact in theabsence of corrosion inhibitors in this medium. Comparisons betweenTrial 17 and 19 revealed that prepassivation is more efficient onceCorrosion Inhibitor 3 is used in this step. Corrosion rate measuredeither by weight loss balance or LPR is lower using a mixture ofCorrosion Inhibitor 1 and Corrosion Inhibitor 3 as precoating additivesthan using Corrosion Inhibitor 1 alone. Visual inspection of thesurfaces of the test coupons in the last three trials did not reveal anylocalized attack indicating that the main component is generalizedcorrosion.

In order to confirm the last results regarding the optimized dosage ofcorrosion inhibitors as well as the resistance of prepassivated film,trials 16, 17 and 18 were repeated under exactly the same conditions.Experimental conditions and weight loss balance are shown in Table 6.LPR results are shown in FIG. 6.

TABLE 6 Experimental conditions and weight loss balance results in seawater environment under adjusted pH. Coupons were precoated usingCorrosion Inhibitor 1 (100 ppm) and Corrosion Inhibitor 3 (50 ppm) withpH adjustment to 8.5. CR 1 CR 3 Adjusted Final Corrosion TrialPrecoating (ppm) (ppm) pH pH* rate (mpy) 20 CR 1 at 100 ppm + 5 2.5 8.488.14 8.3 CR 3 at 50 ppm 21 CR 1 at 100 ppm + 2.5 1.25 8.47 8.12 15.2 CR3 at 50 ppm 22 CR 1 at 100 ppm + — — 8.48 8.13 6.2 CR 3 at 50 ppm *After65 hours trial.

In the foregoing Table, CR 1=Corrosion Inhibitor 1 and CR 3=CorrosionInhibitor 3. LPR results of trial 22 once again revealed that theprecoated film produced using 100 ppm of Corrosion Inhibitor 1 and 50ppm of Corrosion Inhibitor 3 cannot maintain corrosion rates at valueslower than 5 mpy in the absence of a corrosion inhibitor in an aeratedsea water medium. Visual inspection of this coupon also revealed signsof attack on the surface of the metal. Weight loss balance did not agreewith LPR, surface analysis, and Trial 18 data, but it is believed thatan experimental error happened specifically related to this result. Thisspecific result should therefore not be relied upon as indicative of theexpected result. Trial 21 using 2.5 ppm of Corrosion Inhibitor 1 and1.25 ppm of Corrosion Inhibitor 3 under aerated sea water mediumpresented a better corrosion inhibition compared to Trial 22.Nevertheless, LPR data also revealed a strong increase in the corrosionrate at the beginning of the trial followed by variable, but alwayshigh, corrosion rates. This observation indicated that this dosage ofcorrosion inhibitors may not always guarantee good performance in thismedium.

A procedure that presented the outstanding performance in mitigatingcorrosion in mild steel under an aerated sea water environment is theprecoating of the metal surface using Corrosion Inhibitor 1 (100 ppm)plus Corrosion Inhibitor 3 (50 ppm) in sea water at 8.5 pH. Once themetal surface is passivated, the protection against corrosion isprovided by treating the aerated sea water using Corrosion Inhibitor 1(5 ppm) plus Corrosion Inhibitor 3 (2.5 ppm) at 8.5 pH.

The experiments above were carried out using synthetic sea water. Inorder to confirm that these results are valid for real samples, a seriesof long term trials were performed using water samples collected fromthe Pacific and Atlantic Oceans. Real samples from the Pacific Oceanwere tested according to the experimental procedure herein described;precoating the metal surface using Corrosion Inhibitor 1 (100 ppm) plusCorrosion Inhibitor 3 (50 ppm) in sea water at pH 8.5 followed byaddition of Corrosion Inhibitor 1 plus Corrosion Inhibitor 3 at 8.5 pH.Results are shown in Table 7 and FIG. 7.

TABLE 7 Experimental conditions and weight loss balance results in seawater from the Pacific Ocean under adjusted pH. Coupons were precoatedusing Corrosion Inhibitor 1 (100 ppm) and Corrosion Inhibitor 3 (50 ppm)with pH adjustment to 8.5. CR 1 CR 3 Adjusted Final Corrosion TrialPrecoating (ppm) (ppm) pH pH* rate (mpy) 23 CR 1 at 100 ppm + 5 2.5 8.508.33 58.6 CR 3 at 50 ppm 24 CR 1 at 100 ppm + 2.5 1.25 8.53 8.35 61.9 CR3 at 50 ppm *After 114 hours trial.

In the foregoing Table, CR 1=Corrosion Inhibitor 1 and CR 3=CorrosionInhibitor 3. The corrosion inhibition treatment that was successfullyapplied using synthetic sea water did not present the same performancein the presence of sea water from the Pacific Ocean. Corrosion measuredby weight loss balance as well LPR results pointed to a rate higher than45 mpy. Surface visual analysis also shows the presence of localizedcorrosion, especially crevice corrosion. These data indicate that theright dosage for a particular sea water composition must be specificallyoptimized and is not predictable.

Trials using sea water from the Atlantic Ocean were carried out usingthe same prepassivation procedure but with different corrosion inhibitordosages in the sea water. Results are shown in Table 8 and FIG. 8. InFIG. 8, Trial 26 is not depicted due to an error that occurred incarrying out the experiment.

TABLE 8 Experimental conditions and weight loss balance results in seawater from the Atlantic Ocean under adjusted pH. Coupons were precoatedusing Corrosion Inhibitor 1 (100 ppm) and Corrosion Inhibitor 3 (50 ppm)with pH adjustment to 8.5. CR 1 CR 3 Adjusted Final Corrosion TrialPrecoating (ppm) (ppm) pH pH* rate (mpy) 25 — — — 8.21 8.23 99.1 26 CR 1at 100 ppm + 5 2.5 8.50 8.31 64.3 CR 3 at 50 ppm 27 CR 1 at 100 ppm + 105 8.49 8.33 10.2 CR 3 at 50 ppm 28 CR 1 at 100 ppm + 20 10 8.50 8.31 3.6CR 3 at 50 ppm *After 68 hours trial.

In the foregoing Table, CR 1=Corrosion Inhibitor 1 and CR 3=CorrosionInhibitor 3. Results using sea water from the Atlantic Ocean confirmedthat it is possible to mitigate corrosion in a sea water environmentunder air by using corrosion inhibitors. Data of weight loss balance andLPR demonstrate that there could be an optimal dosage of inhibitor thatis able to mitigate and stabilize the corrosion rate. For syntheticseawater, Corrosion Inhibitor 1 (5 ppm) plus Corrosion Inhibitor 3 (2.5ppm) dosages are enough to prevent corrosion after pre-passivation,while this dosage had to be increased in order to achieve the sameresults in sea water samples from the Atlantic Ocean. The use ofCorrosion Inhibitor 3 along with Corrosion Inhibitor 1 is an effectiveanticorrosive treatment for sea water and the right dosage of theseproducts should be optimized according to the environment that the mildsteel will be in contact with.

All of the compositions and methods disclosed and claimed herein can bemade and executed without undue experimentation in light of the presentdisclosure. While this invention may be embodied in many differentforms, there are described in detail herein specific preferredembodiments of the invention. The present disclosure is anexemplification of the principles of the invention and is not intendedto limit the invention to the particular embodiments illustrated. Inaddition, unless expressly stated to the contrary, use of the term “a”is intended to include “at least one” or “one or more.” For example, “adevice” is intended to include “at least one device” or “one or moredevices.”

Any ranges given either in absolute terms or in approximate terms areintended to encompass both, and any definitions used herein are intendedto be clarifying and not limiting. Notwithstanding that the numericalranges and parameters setting forth the broad scope of the invention areapproximations, the numerical values set forth in the specific examplesare reported as precisely as possible. Any numerical value, however,inherently contains certain errors necessarily resulting from thestandard deviation found in their respective testing measurements.Moreover, all ranges disclosed herein are to be understood to encompassany and all subranges (including all fractional and whole values)subsumed therein.

Furthermore, the invention encompasses any and all possible combinationsof some or all of the various embodiments described herein. It shouldalso be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the invention and withoutdiminishing its intended advantages. It is therefore intended that suchchanges and modifications be covered by the appended claims.

What is claimed is:
 1. A method of mitigating corrosion of a conduitcontaining an aqueous medium comprising: (a) providing a metal conduit;(b) introducing an aqueous medium into said metal conduit; (c) injectinga mixture comprising an effective amount of one or more transitionmetals, one or more organic phosphates, and one or more inorganicphosphates into said aqueous medium; (d) injecting an effective amountof hydroxyphosphono acetic acid and/or salts thereof into said aqueousmedium, (e) treating said metal conduit with an effective amount of amixture comprising one or more transition metals, one or more organicphosphates, and one or more inorganic phosphates before step (b); and(f) treating said metal conduit with an effective amount ofhydroxyphosphono acetic acid and/or salts thereof before step (b). 2.The method of claim 1, wherein said effective amount in step (e) isabout 100 ppm and said effective amount in step (f) is about 50 ppm. 3.The method of claim 1, further comprising the step of adjusting a pH ofthe aqueous medium to about 8.5 by adding lime or soda ash.
 4. Themethod of claim 1, wherein said effective amount in step (c) is fromabout 5 ppm to about 20 ppm and said effective amount in step (d) isfrom about 2.5 ppm to 10 ppm.
 5. The method of claim 1, wherein saidaqueous medium is sea water.
 6. The method of claim 1, wherein said oneor more transition metals comprises zinc.
 7. A method of mitigatingcorrosion of a conduit containing an aqueous medium comprising: (a)providing a metal conduit; (b) introducing an aqueous medium into saidmetal conduit; (c) injecting a mixture comprising an effective amount ofone or more transition metals, one or more organic phosphates, and oneor more inorganic phosphates into said aqueous medium; and (d) injectingan effective amount of hydroxyphosphono acetic acid and/or salts thereofinto said aqueous medium, wherein said aqueous medium is sea water.
 8. Amethod of mitigating corrosion of a conduit containing an aqueous mediumcomprising: (a) providing a metal conduit; (b) introducing an aqueousmedium into said metal conduit; (c) injecting a mixture comprising aneffective amount of one or more transition metals, one or more organicphosphates, and one or more inorganic phosphates into said aqueousmedium, wherein said one or more transition metals comprises zinc; and(d) injecting an effective amount of hydroxyphosphono acetic acid and/orsalts thereof into said aqueous medium.